1. Field of the Invention
This invention relates generally to mechanical printingxe2x80x94as opposed to manual printing of the type which might be carried out with pen and ink on paper. Thus, this invention relates to inkjet printing. More particularly, this invention relates to a method used to control one or more print heads in an inkjet printer, and to an inkjet printer utilizing this method.
2. Related Technology
One form of conventional inkjet printer or plotter typically has a print cartridge mounted on a movable carriage. This carriage is traversed back and forth across the width of a print media (i.e., usually paper or a plastic plotting film, for example) as the print media is fed is through the printer or plotter. Plural orifices on a print head of the print cartridge are fed ink (or other printing fluid) by one or more channels communicating from a reservoir of the print cartridge. Energy applied individually to addressable resistors (or to other energy-dissipating elements, for example, to piezoelectric actuators), transfers energy to ink or other printing fluid at the print head; which ink (printing fluid other than ink hereinafter being subsumed also in the term xe2x80x9cinkxe2x80x9d) is within or associated with selected ones of the plural orifices. These orifices then eject a part of the ink onto the printing media. The ejected ink forms a fine-dimension jet or stream that impinges on the printing media at a selected location dependent upon the relative positions of the print media and of the selected orifice(s) from which ink is ejected.
Another form of conventional inkjet printer has a media transport mechanism that controllably moves print media past an array of plural print cartridges, each with a respective print head. In this type of inkjet printer, the print cartridges are arrayed in a stationary array, usually of xe2x80x9cblock wallxe2x80x9d arrangement, or in a diagonally arrayed and slightly overlapped arrangement, so that the entire width of the print media (or of that portion of the print media on which printing is to be done) passes by the print heads as the media is controllably moved through the printer.
Viewing now PRIOR ART FIGS. 7 and 8, and with attention first to FIG. 7, it is seen that in a conventional inkjet printer 500 (of either the first type or the second type described above), a sheet of printing media 502 is controllably moved generally along a media transport direction, indicated by arrow 504 (for the first type of conventional inkjet printer) or in the direction of arrow 506 (for the second type of conventional inkjet printer).
In the first type of conventional inkjet printer, a print cartridge having a print head 508 scans across the media 502 in a direction generally perpendicular to the direction 504 of media transport. As this print head 508 scans across the print media, ink is discharged from selected ones of plural printing orifices 510. The print head 508 may make plural successive printing scans in the same direction (returning to a selected starting position after each scan), which plural scans are coordinated with advancement of the print media 502 along line 504. Alternatively, the print head 508 may make bi-directional printing scans, in which ink is ejected during scans of successively opposite directions.
In FIG. 7, bi-directional printing scans of the print head 508 are represented by the oppositely directed arrows 512, 514, and 516. The arrow 512 associated with printing xe2x80x9cswathxe2x80x9d 512a indicates a representative xe2x80x9cfirstxe2x80x9d printing scan in the indicated direction. The plural orifices 510 may place ink in this swath 512a. Thus, on the next-successive printing scans 514, 516 the position of the print head 508 relative to the media 502 is indicated by the numerals 508xe2x80x2, and 508xe2x80x3 (with the media having been moved by the media transport mechanism to print in swath 514a, then in swath 516a) and with the print head 508 successively moving in opposite directions. It is to be noted in FIG. 7 that the print head 508 appears to have a slight angularity (i.e., at the line of orifices 510) with respect to the direction of scanning represented by arrows 512, 514, and 516. That is, the line of the plural orifices 510 is not truly perpendicular to the direction of scanning represented by arrows 512, 514, and 516. This apparent angularity is further explained below.
In the second type of conventional inkjet printer, also illustrated by FIG. 7, the print media moves in the direction 506, and an array of print heads 508, 508xe2x80x2, and 508xe2x80x3 (now referring to individual print heads, and not to successive alternative positions of a single print head) are arranged in a diagonal array, and are slightly overlapped with one another, so that the plural printing orifices 510, 510xe2x80x2, and 510xe2x80x3 of the print heads provide substantially full printing coverage of the print media. That is, each of the printing swaths 512a, 514a, and 516a is covered by one of the lines of orifices as the media 502 moves past these print heads. Again, it will be noted that the print heads 508, 508xe2x80x2, and 508xe2x80x3 are somewhat angulated (i.e., with respect to the lines of orifices 510, et al) relative to perpendicularity to the direction of media movement 506.
With either type of angularity explained above (i.e., either in a single print head scanned across print media, or in plural print heads past which media is moved) an effect of the angularity is that an elongate line that parallels the lines 510 of orifices, which is composed of plural line segments, and which line is supposed to be straight over its length, will be printed as somewhat disconnected, but parallel line segments. That is, the line segments 518 and 520 are aligned so that their centroids 518a and 520a align with one another in the direction that the line segments 518 and 520 are supposed to extend. However, because of the angulation discussed above, the adjacent line segments 518 and 520 are not perfectly aligned with one another, and are not perfectly connected. This lack of perfect connection of the line segments 518 and 520 produces a xe2x80x9ccuspxe2x80x9d or visual angularity artifact 522 (i.e., a xe2x80x9cjaggednessxe2x80x9d of the line including the segments 518 and 520). The apparent angulation existing in the conventional printer 500 and creating visual artifacts 522 may result from a number of causes.
Importantly, a xe2x80x9ctime-of-flightxe2x80x9d correction, which is commonly provided in conventional inkjet printers does not contribute to the artifact 522, and will not remove the artifact 522. Thus, correction of a xe2x80x9ctime of flightxe2x80x9d factor for bi-directional printing (i.e., in a printer of the first type described above) will not eliminate the artifacts 522. Further, visual artifacts 522 appear in angulated lines as well. Viewing PRIOR ART FIG. 8, it is seen that visual artifacts (each indicated with numeral 522) are present in a number of lines that should be straight (but which appear jagged to a greater or lesser degree).
Importantly, this apparent angulation may result from a lack of true perpendicularity between the direction of print head scanning and the direction of print media advance through the printer. Also, apparent angulation can result from true misalignment between the array of orifices 510 and the direction of print head scanning (as in the first type of inkjet printer explained above), or from a xe2x80x9cglobalxe2x80x9d misalignment of the print heads, as in the second type of ink jet printer explained above. Efforts to eliminate these apparent angularities from inkjet printers have not proven successful. Particularly, an apparent angularity that results form a xe2x80x9cskewxe2x80x9d angle of print media moving through a printer is particularly difficult (i.e., impossible) to eliminate. Such a print media xe2x80x9cskewxe2x80x9d may result from a multitude of factors that are difficult to control. For example, a slight build up of paper fibers on the rollers that move paper along the printing path of a printer can result in slight paper slippage, in a slight difference in effective diameter among the plural rollers, and may result in a slight angulation of the paper movement relative to true perpendicularity with the scan direction of the print head.
Further considering PRIOR ART FIG. 7, it is to be understood again that the apparent angularity of the print head(s) is for purposes of illustration, is exaggerated in comparison to the angularity that may conventionally exist in known inkjet printers, and is also to be taken as representative of a possible angularity (i.e., lack of true perpendicularity) between either the direction of arrows 512, 514, and 516, and the direction indicated by the arrow 504; or an angularity (i.e., lack of true perpendicularity) between the print heads and the direction of print media advance through the printer.
PRIOR ART FIG. 7 also depicts diagrammatically a conventional expedient that has been attempted to compensate for the visual artifacts 522. That is, viewing the right-hand portion of PRIOR ART FIG. 7, it has been suggested to offset adjacent line segments 524 and 526 by a distance xe2x80x9cXxe2x80x9d such that the angulated line segments connect properly with one another, and so that a visual artifact (like artifact 522) is not created between these line segments. However, the same conventional teaching maintains that the vertical line that includes segments 524 and 526 is to be kept vertical, so that a next-successive line segment 530 is printed at a location such that its centroid 530A is aligned with the centroid 524A of the line segment 524. Thus, as PRIOR ART FIG. 7 shows, the result of this conventional expedient is to eliminate some visual artifacts, at the cost of accentuating other visual artifacts, such as the one indicated at 532 on PRIOR ART FIG. 7.
It would be an advantage in the art if a way were available to compensate for apparent angularities in inkjet printers, and to eliminate visual artifacts resulting from such apparent angularities.
In view of the deficiencies of the related technology, an object for this invention is to reduce or overcome one or more of these deficiencies.
A further object is to provide a method and apparatus for inkjet printing in which visual artifacts resulting from apparent angularity between a print head (or print heads) and a print media are reduced or substantially eliminated.
Other objects, features, and advantages of the present invention will be apparent to those skilled in the pertinent arts from a consideration of the following detailed description of a single preferred exemplary embodiment of the invention, when taken in conjunction with the appended drawing figures, which will first be described briefly.